1. Field of the Invention
The present invention relates to a coating treatment apparatus and a coating treatment method each for applying, into a thin film state, a coating solution containing a coating film forming component and a solvent onto the front face of, for example, a square substrate such as a mask substrate.
2. Description of the Related Art
In a manufacturing process of a semiconductor device and an LCD, processing using a photolithography technique is performed. This processing is performed by a series of steps of applying a predetermined coating solution such as a resist, into a thin film state, onto the front face of, for example, substrates to be processed such as a semiconductor substrate and a mask substrate made of glass and drying it to form a film, and thereafter exposing the substrate to light and then performing developing treatment on the substrate to obtain a desired pattern.
Methods of forming, for example, a thin film of a resist on the front face of a square substrate being one of the aforementioned substrates to be processed, include a well-known method by spin coating. The spin coating will be briefly described using FIG. 13.
In the drawing, a numeral 1 denotes a sp 1 in chuck for holding, in a horizontal posture, for example, a square substrate G such as a mask substrate, and a coating solution nozzle 11 is provided at a position slightly above the center portion of the front face of the substrate G on the spin chuck 1. Then, when the substrate G is rotated about the vertical axis by the spin chuck 1 and, for example, a coating solution (resist solution) made by mixing a resist component and a solvent such as a thinner is supplied onto the front face of the substrate G, the coating solution spreads over the entire front face of the substrate G by the effect of a centrifugal force, resulting in a solution film in a thin film state formed on the substrate G.
Subsequently, after the supply of the coating solution is stopped, a so-called spin drying is performed in which the substrate G is further rotated to allow the thinner to evaporate, whereby the resist component remains on the substrate G, thus forming a resist film. In the spin coating, as described above, the substrate G is rotated so that the coating solution is spread into a thin film state with an excessive coating solution spun off.
Incidentally, when a coating film is formed on the front face of a square substrate using the spin coating method described above, there occurs a difference in circumferential speed between the center portion and the peripheral portion which are different in radius of gyration. Further, in a schematic description, there exists a swirl of solvent vapor evaporating from the coating solution within a circular region touching internally the substrate G during the spin coating, but a swirl above a passing region at corner portions lying off the circular region becomes a swirling flow with much fresh air taken-in because they are located outside the aforementioned swirl, so that the volatilization rate of the solvent at the corner potions is higher than that inside. As described above, if there is a difference in evaporation rate of the solvent between the corner portions and the center portion, a coating film 12 formed on the front face of the substrate has a shape specific to the square substrate in which the film thickness rises higher at the corner portions than at the center portion as schematically shown in FIG. 14. The coating film in such a shape is not usable in some cases because it affects exposure and development, leading to a decrease in yield of substrate.
One of measures to this problem has been reported, for example, as shown in FIG. 15, in which a gas flow restraining ring 14 is provided on an inner periphery of a cup 15 surrounding the substrate G in a manner to face the front face at the corner portions of the substrate G, whereby the evaporation rate of the solvent at the corner portions of the substrate G is restrained to uniformize the film thickness (for example, in a first embodiment of Japanese Patent Application Laid-open No. Hei 11-70354, FIG. 2).
In such a conventional technique, since the cup 15 is being exhausted and the substrate G is being rotated, a gas flow (downflow) from above the cup 15 toward the front face of the substrate G is formed, in which a gas flow restraining ring 14 is provided to restrict to inside the corner portions of the substrate G the region against which the downflow hits, thereby increasing the concentration of the solvent vapor of the swirling flow within the passing region at the corner portions so as to suppress the evaporation of the solvent at the corner portions to decrease the rise of the film.